1. Field of the Invention
The present invention relates to the field of computer systems. In particular, the present invention relates to field upgrading the processor of a computer system.
2. Background Information
As microprocessor technology continues to evolve in a faster and faster pace. Purchasers of microprocessor based computer systems demand better performance scalability from the system manufacturers to protect their investment. A particular aspect of performance scalability is the ability to field upgrade the original microprocessor to at least one newer generation of microprocessor.
FIG. 1 illustrates a typical prior art approach to field upgrading the microprocessor of a computer system. The original microprocessor package 10 is surface mounted onto a main circuit board 14, also known as the motherboard. For the illustrated embodiment, the original microprocessor package is a rectangular plastic quad flat pad (PQFP) package having connecting leads 32 extending outward along the perimeter. The leads 32 are soldered to physically and electrically connect with a land grid pattern (not shown) pre-disposed on the motherboard 14. The land grid pattern in turn is physically and electrically connected to the interconnect wiring circuitry (not shown) embedded "inside" the motherboard 14.
A processor upgrade socket 12 (hereinafter, upgrade socket) having the proper electrical "connectors" 28 designed to receive and mate with an upgrade microprocessor package (not shown), is wave soldered onto the motherboard 14 in a vicinity immediately adjacent to the surface mounted original microprocessor package 10. For the illustrated embodiment, the upgrade socket 12 is a zero insertion force (ZIF) upgrade socket having three major parts, the base portion 16, the top portion 18, and a lever mechanism 20. Each of the base as well as the top portions 16 and 18 has a center cut out 24. The electrical "connectors" 28, which are receptacle holes for the illustrated embodiment, are disposed in part in the base portion 16, and in part in the top portion 18. The bottom portion 16 further includes a number of connecting pins (not shown) disposed on its bottom surface 30. These connecting pins are wave soldered through the motherboard 14, making contacts with the embedded interconnect wiring circuitry inside the motherboard 14.
Furthermore, the top portion 18 is adapted to laterally "slide" on top of the bottom portion 16. The lateral sliding movement is controlled by the lever mechanism 20. The upgrade socket 12 is illustrated in an "open" position. The upgrade socket 12 is laterally "slid" into a "closed" position after the upgrade microprocessor package is mounted onto the upgrade socket 12 by having its pins inserted into the receptacle holes 28. At the "closed" position, the center cut outs 24 as well as the two portions of each of the receptacle holes 28 are aligned, securing the physical as well as the electrical contacts between the pins of the upgrade microprocessor package and the receptacle holes 28 of the upgrade socket 12. The amount of lateral "sliding" going from the "open" position to the "close" position is very small (1-2 cm). The amount of lateral displacement shown, as evident by the amount of exposed lower portion 26a and 26b, is exaggerated for illustrative purpose.
In other words, the original microprocessor package 10 and the upgrade socket 12 are disposed side by side to each other on the motherboard 14. This side by side approach has the advantage that the upgrade microprocessor may operate as a co-processor to the original microprocessor, since the upgrade microprocessor will not be obstructing thermal dissipation of the original microprocessor, turning the computer system into a multi-processor system. However, this advantage is enjoyed by few systems, since the overwhelming majority of field upgraded systems remain uniprocessor systems.
On the other hand, this side by side approach has the disadvantage that more than twice the amount of motherboard real estate are required, when compared to the historic case where field upgradability is not provided. As the scale of integration continues to increase, more traditional add-on functions such as video add-on cards are being integrated as standard functions of the motherboard 14 and compete for the same scarce motherboard real estate. Another disadvantage is the long trace lengths required between the original CPU and the upgrade CPU, which can become a problem for the emerging faster processors requiring immediate access to the "off-chip" cache memory. Thus, it is increasing desirable to be able to provide an alternative approach to CPU field upgradability requiring less motherboard real estate, especially when the "multi-processor" advantage is seldom exploited.
As will be disclosed in more detail below, the present invention provides for methods and apparatus for providing processor field upgradibility to a motherboard that achieves these and other desirable results.